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The MBWrite Function Block is edge triggered and the address can be changed dynamically. You only need one MBWrite. Set the start address and then trigger the Write command.

However, something seems wrong about only being able to write one coil. Single shot write commands is not really how Modbus is supposed to work. Remember that you can write multiple "coils" by writing Registers to the same address.

Problem is having 200 Digital outputs, chances are that two operator can operate the systems. So may be we required to have multiple MBWrites to be used .
These are the default function of SCADA system (Microscada) event i think similar configuration is for the Foxbro DCS.